Auto racing of all kinds has become increasingly popular and increasingly competitive. The highly competitive nature of the sport requires each racing team to push the limits of speed and performance in every respect. When fine tuning performance (to thus optimize speed), it is desirable to eliminate or control as many variables as possible.
Tire traction is key to the “handling” of a race car and it is well known that both tire temperature and pressure greatly affect traction. The goal of adjusting tire pressures is to maximize the overall handling grip of the car. Top professional racing teams sometimes make very minor adjustments to tire pressure (in increments as small as ¼ psig) in an attempt to optimize traction, performance, handling, and speed.
It is well known that as a car is driven, the temperature of the tires increases from the “cold” (ambient) temperature, heating the air within the tire and causing the pressure of the air to increase. Likewise, changes in ambient temperature affect the “cold” temperature of the tires and can have a significant effect on the baseline or “cold” pressure. Ambient or cold temperatures may vary greatly from race day to race day over the course of a race season that lasts several months and covers many geographically diverse cities. Moreover, ambient temperatures may vary significantly during a single day and during the duration of a single race. A cool cloudy morning, when tire inflation is first set, often develops into a hot sunny day (and vice-versa). Even in a stack of tires in the pit area, some may be exposed to full sun while others are shaded. The effect can easily be 10° F. or more. More significantly, the race crew is not likely to know the actual temperature variation of any given situation.
Although not wholly accurate, a change of 10° F. equating to a change in tire pressure of about 1 psig has been used as a “rough estimate.” Being able to quantify this variable, rather than relying on rough estimates or guesswork, could make such minor tire pressure adjustments more effective and useful.
One method proposed for stabilizing tire pressure relative to temperature change is to fill the tire with substantially pure and dry nitrogen (N2) gas, rather than common air, such as taught by U.S. Pat. Nos. 5,878,791; 6,155,313; 6,374,869; and 6,470,923. This approach ignores that nitrogen is equally affected by temperature according to the ideal gas law (since the number of molecules remains constant) and that water is readily drawn out of the tire compound itself such that humidity may be restored inside the tire within a matter of hours.
Another way of maintaining an essentially constant tire pressure despite temperature increases is by using a wheel mounted relief valve, such as shown in U.S. Pat. No. 4,246,930, issued Jan. 27, 1981. Unfortunately, the use of such devices have been banned by certain tracks and racing leagues. There has also been some question raised about whether these valves will function properly when subjected to the extreme centrifugal force produced at speeds in excess of 200 miles per hour. Also, these valves are not able to compensate for ambient temperature decreases.